Bill St. John Wilkes, The Handbook of Underwater Exploration, Stein and Day, 1971

USE OF BUOYANCY BAGS

The conventional lifting bag is pear-shaped in design and usually made from either very strong canvas or a Neoprene fabric. The lifting lines are generally broad web bands that pass right over the top of the bag and are securely sewn to it for their entire length of contact. These end some 30-50cm below the open mouth of the bag which is at the narrow end of the inverted pear. Such bags have lifting capacity according to their size, arer easily handled, and take very little space when not in use.

The bag is made pear-shaped so that air can escape, but it will come from a narrow opening directly under the centre of the bag and cannot therefore upset the b alance or stability of the device. Additionally, the load is less likely to swing about, again because it is secured immediately under the centre of gravity. In principle there are no problems with using these bags; in practice, it pays to experiment before starting a serious lifting operation.